Question: Luis is 28 years younger than Tiffany. For the last four years, Tiffany and Luis have been going to the same school. Nineteen years ago, Tiffany was 5 times as old as Luis. How old is Tiffany now?
Answer: We can use the given information to write down two equations that describe the ages of Tiffany and Luis. Let Tiffany's current age be $t$ and Luis's current age be $l$ The information in the first sentence can be expressed in the following equation: $t = l + 28$ Nineteen years ago, Tiffany was $t - 19$ years old, and Luis was $l - 19$ years old. The information in the second sentence can be expressed in the following equation: $t - 19 = 5(l - 19)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $t$ , it might be easiest to solve our first equation for $l$ and substitute it into our second equation. Solving our first equation for $l$ , we get: $l = t - 28$ . Substituting this into our second equation, we get the equation: $t - 19 = 5($ $(t - 28)$ $ -$ $ 19)$ which combines the information about $t$ from both of our original equations. Simplifying the right side of this equation, we get: $t - 19 = 5t - 235$ Solving for $t$ , we get: $4 t = 216$ $t = 54$.